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Panel Voltages


viper_za
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I finally had some time to install my 3 Panels on the roof over the weekend.

3x ReneSola Virtus II 300W panels connected in series

Spec of the panels

Maximum Power (Pmax) : 300W
Power Tolerance : 0 ~ +5W
Module Efficiency : 15.5%
Maximum Power Current (Imp) : 8.20A
Maximum Power Voltage (VMP) : 36.6V
Short Circuit Current (Isc) : 8.69A
Open Circuit Voltage (Voc) : 44.8V

 

The panels are not connected to anything yet except the combiner box so far.

Tested with the multimeter and got the following readings yesterday when we had some clear skies with only a cloud now and then.

8:30 AM:   125V and 5.58A

11:30 AM: 125.8V and 9.5A (This scared and impressed me with the multimeter only being rated to 10A)

After this i just measured voltage every now and then mostly at around the 121-126v mark too scared i blow my multimeter on amps.

 

What I am wondering is should I not get close to 3x Voc (44.8 x 3 = 134.4V) on clear skies?

 

Thanks for any feedback

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I think temperature is the defining factor here. On a cold morning with bright sunshine you get these insane open circuit voltages. The Voc quoted on the panel is likely such an extreme value that you might never see in this part of the world :-)

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For every 1 oC rise above 25oC each panels will lose 0.13V VOC (loss on the string 0.39V) . On a hot day your panels could be anything between 50 - 70 oC. This is important in winter as those 3 panel in series could potentially have a VOC of 146.4 V (@ -5 oC). It is unlikely but it is something to bear in mind when looking at your MPPT's max voltage.

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For every 1 oC rise above 25oC each panels will lose 0.13V VOC (loss on the string 0.39V) . On a hot day your panels could be anything between 50 - 70 oC. This is important in winter as those 3 panel in series could potentially have a VOC of 146.4 V (@ -5 oC). It is unlikely but it is something to bear in mind when looking at your MPPT's max voltage.

These are the Axpert Voltages

MPPT Range @ Operating Voltage: 60VDC ~115VDC

Maximum PV Array Open Circuit Voltage: 145 VDC

If I workout for the string according to spec

VMP: 36.6 x 3 = 109.8V
VOC: 44.8 x 3 = 134.4V
 
Live in Pretoria and almost never see -temps.
In the range but just, should I be worried about damage to the inverter?
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Live in Pretoria and almost never see -temps.
In the range but just, should I be worried about damage to the inverter?

 

It is unlikely. At 0oC your winter VOC max would be about 145V. However you would need there to be no draw and below freezing and  have  an irradiance of 1000W/m2. Early in the morning when it is cold, and your are at risk, your batteries should accept charge (so there would be a draw) and you unlikely to have 1000W/m2 at 8 in the morning.  My winter VOC max is about 128V DC. The highest I have seen is about 109 oC. There is a risk your panels could exceed 145V DC but I think that risk is small. One could switch off your PV input if you are expecting extreme cold. I have a DC circuit breaker in the house where I can isolate the PV input and measure the voltage without having to step outside and be exposed to the elements.  

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It is unlikely. At 0oC your winter VOC max would be about 145V. However you would need there to be no draw and below freezing and  have  an irradiance of 1000W/m2. Early in the morning when it is cold, and your are at risk, your batteries should accept charge (so there would be a draw) and you unlikely to have 1000W/m2 at 8 in the morning.  My winter VOC max is about 128V DC. The highest I have seen is about 109 oC. There is a risk your panels could exceed 145V DC but I think that risk is small. One could switch off your PV input if you are expecting extreme cold. I have a DC circuit breaker in the house where I can isolate the PV input and measure the voltage without having to step outside and be exposed to the elements.  

Thanks Chris, also have the combiner in the house with a breaker for the string for just incase :)

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Thanks Chris, also have the combiner in the house with a breaker for the string for just incase :)

 My combiner is outside and have 17 m of 25mmarmoured cable running from the combiner box into the house. 40 A DC circuit breaker between armoured cable and the inverter. The thing with safety isolators is that you probably never use them but there comes a day, if you did not install them, that you wished you had installed them. 

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  • 1 month later...

Max PV today has so far reached 736W (of Panel Max of 600W (2x300)) 2x ReneSola Virtus II 300W

 

Thats 22.6% better than spec.

 

Temp is around 25 deg with scattered cloud.
 

Nice - but does raise issues around fully populating the inverter (Axpert 5/48V) with 3000W of panels... (could get 3650W)??

 

Regards

Mark

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Max PV today has so far reached 736W (of Panel Max of 600W (2x300)) 2x ReneSola Virtus II 300W

 

Thats 22.6% better than spec.

 

Temp is around 25 deg with scattered cloud.

 

Nice - but does raise issues around fully populating the inverter (Axpert 5/48V) with 3000W of panels... (could get 3650W)??

 

Regards

Mark

As long as you do not exceed the 115 VDC of the MPPT (inverter max 145 VDC)  you should be fine. The inverter will not use more than 3kW even if you produce more than this.

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  • 3 weeks later...

Max PV today has so far reached 736W (of Panel Max of 600W (2x300)) 2x ReneSola Virtus II 300W

 

Thats 22.6% better than spec.

 

Temp is around 25 deg with scattered cloud.

 

Nice - but does raise issues around fully populating the inverter (Axpert 5/48V) with 3000W of panels... (could get 3650W)??

 

Regards

Mark

Ok today I achieved my MaxPV so far...778W (129%) off my 600W pf panels

 

Scattered cloud and about around 26%

 

Amazed...

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You can't really measure efficiency without also measuring insolation. Panels are rated at a standard 1000w per square meter, but sometimes the sun does better than that, especially if you have clouds to reflect some light off. I've also recorded 20% above rating on such days. Mostly though... It's hotazel and they make maybe 90% of their capacity.

Sent from my GT-I9195 using Tapatalk

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